Automotive glazings (e.g., windshields, backlites, etc.) typically include first and second glass substrates (also sometimes referred to as lites or plies) that are heated and bent to form a desired shape and then laminated to one another using a polymer-based or plastic interlayer (e.g., Poly Vinyl Butyral (PVB), ethyl vinyl acetate (EVA), and/or the like).
Devices and methods for heat bending glass sheets are well known in the art. For example, see U.S. Pat. Nos. 7,140,204; 6,318,125; 6,158,247; 5,443,669; and 5,383,990, the entire contents of which are hereby incorporated herein.
Processes to bend vehicle windshields include “double lite bending” and “single lite bending.” In a double lite bending process, the two substrates are separated slightly, for example, by a powder layer and gradually heated to approximately 600 to 640 degrees C. and bent to form the desire shape. The powder layer may be composed of a material that remains inert at the process temperature range. The two bent substrates are then laminated to one another. In single lite bending process, each substrate is separately heated and bent before being laminated together.
Double lite bending is often preferred over single lite bending, especially in cases where the windshields have higher levels of curvature, e.g., because there is an improved probability of there being a good mutual fit of the substrates that, in turn, may result in higher quality optics and quality of lamination. By contrast, bending the substrates separately, even when formed using the same tools, has been found to reduce the probability of a good match. In this regard, it is known that forming on the same tool generally creates a mismatch of shape, as the laminated surfaces typically will be offset by at least the glass thickness. For instance, usually surface 2 and 4 have touched the tool in a single lite process, so surfaces 2 and 3 generally will not have the exact same curvature. Single lite bending processes oftentimes also are further limited in their ability to create windshields having differing substrates in terms of thickness and/or color/tint.
FIGS. 1-6 illustrate a prior art technique for making an automotive glazing with a screen printed opaque pattern using a double lite bending process. Referring to FIG. 1, the screen printing process includes a first glass substrate 10 screen printed in connection with a silk-screen drum 12 and wiper or doctor blade 13. The silk-screen drum 12 and wiper or doctor blade 13 cooperate to print an opaque material 11 onto a surface of the substrate 10 in a desired pattern. It is noted that as an alternative to printing drums, substantially flat, two-dimensional silk-screens sometimes are stretched into metal frames, with a silk-screen being stationary and a squeegee and flood bar being passed mechanically over the screen. The desired pattern oftentimes includes a solid or stylized frame around one or more edges of the substrate, e.g., to help conceal mounting brackets, sensors and/or other electronic devices, electrical connections, serve as a decorative perimeter band, protect the mounting adhesive from exposure to ultraviolet light and degradation, function as a solar control coating, etc.
The opaque material 11 may be of or include, for example, a ceramic frit. As is known, ceramic frits typically are composed of ground glass with a specific softening point combined with metals and oxides (e.g., bismuth (and/or an oxide thereof), nickel (and/or an oxide thereof), chromium oxide, cobalt oxide, and/or nickel oxide, etc.) to attain the desired color (often a dark or black color), adhesion properties, durability, etc.
Referring to FIG. 2, the screen-printed substrate 10′ includes a screen-printed opaque layer 14. The screen-printed opaque layer 14 may be used, for example, on windshields, side lites, and/or backlites. The opaque layer 14 in the FIG. 2 example is applied to peripheral areas of the first substrate 10 to form a decorative perimeter band and to protect the mounting adhesive from exposure to ultraviolet light and degradation. The opaque layer 14 in this example may also be used to display a Department of Transportation (DOT) code and/or trademark, to hide trim components and/or sensor mounts, etc., as is conventional.
Ceramic frits may be suspended in a medium (for example, a medium of or including oils or water) to allow printing of the patterns in liquid form. The medium may include volatile materials. Accordingly, the screen-printed substrate 10′ that includes the opaque layer 14 may first be introduced into a drying oven 15 as shown in FIG. 3 to pre-cure the opaque layer 14 and remove a majority of the medium before the screen-printed substrate 10′ is introduced into the bending furnace or lehr (e.g., as shown in FIG. 5). Otherwise, introducing wet frit into the bending furnace may cause the volatile medium to flash off and contaminate the bending furnace, create craters or pinholes related to excessively rapid drying of the film, increase the risk of contamination of the wet material, and/or create difficulty in handling the wet-applied materials.
The drying oven 15 that pre-cures the opaque layer 14 may use any source of heat (for example, infrared or convection) or may substantially remove the volatile materials through ultraviolet radiation.
Once the applied opaque material 14 is dried via the pre-curing process, the screen-printed substrate 10′ may be stacked with a second substrate 20 as illustrated in FIG. 4. The screen-printed substrate 10′ and the second substrate 20 may be introduced into a bending furnace as illustrated in FIG. 5. Heat 30 is applied to soften the substrates so they can be bent, e.g., in a bending mold or frame. The screen-printed substrate 10′ and the second substrate 20 are then separated and a laminating material 40 (e.g., PVB) is applied as illustrated in FIG. 6.
In selecting a material to form the opaque layer 14, a water- or oil-based frit sometimes will have adequate green strength (e.g., the initial adhesive strength of a material that allows it to be handled before it has completely cured or fired) to undergo typical handling operations before the bending and firing process illustrated in FIG. 5 if the screen-printed substrate 10′ is pre-cured as illustrated in FIG. 3, e.g., to temperatures of approximately 270 to 380 degrees F. (132 to 193 degrees C.) when thermal drying systems are used. Although pre-curing the frit in this temperature range may provide an adequate green strength to enable the substrate with the material thereon to undergo typical handling prior to and/or in preparation for bending and/or firing processes, pre-curing the frit in this temperature range may still present several challenges. For example, because the dried frit is not permanently bonded to the glass substrate 10 at this point, it may be easily and potentially inadvertently scratched off, chipped away, and/or otherwise removed in whole or in part.
If there is a significant amount of frit present, volatiles may remain even after the pre-curing process. If the frit is on a glass surface exposed to the atmosphere of the furnace or lehr, the volatiles may simply escape to the environment as a result of the high temperatures associated with the bending processes. However, if the frit is between two glass substrates as illustrated in FIG. 5 (and for example, separated slightly by a powder layer as described above), the remaining volatiles may try to escape from the edges between the glass substrates 10 and 20. Unfortunately, however, these fumes may be partially or fully trapped, causing fogging and/or staining of the glass substrate surfaces. In some situations, the inability of the volatiles to completely escape and/or their tendency to build up on an inner surface may therefore lead to a disadvantageous aesthetic appearance.
Additionally, in order to achieve correct firing, the frit generally will need to pass through a softened state, during which there is a possibility that the liquidus frit will locally bond or fuse together the glass substrates 10′ and 20, as even the separator powder oftentimes will be absorbed or saturated by the frit. It has been observed that even small fused areas may result in immediate or subsequent glass fractures, thereby reducing yield. This phenomenon oftentimes is exacerbated at areas of the substrates that are under high pressures, e.g., because of their shapes, contact with support or press tools, etc.
Attempts have been made to develop a “direct fire” solution. Such attempts generally have in the past attempted to use frit materials that have the lowest possible amount of volatiles prior to the substrates entering the bending furnace, while also having firing and/or softening points selected to try to avoid having the material be soft at times where pressures and/or relative motion of the plies are relatively high. In practice, this balance is very difficult to achieve, as the frit ultimately must be properly fired without driving a need to either under- or over-bend the windshield as a result of too much total heat. Indeed, as will be appreciated by those skilled in the art, this balance has made conventional direct fire surface 2 and surface 3 frit solutions unreliable and thus ill-suited for use in an everyday manufacturing environment.
Instead of pre-curing the frit in the lower temperature range described above, common solutions for double lite bending operations needing surface 2 frit applications involves printing a traditional frit while the substrate is in a flat state and pre-firing the frit at elevated temperatures of approximately 560 to 600 degrees C. (1040 to 1112 degrees F.). In this process, the risk of outgassing is reduced, as the volatiles and organics may be completely removed through the elevated temperatures. At such high temperatures, the frit likely will cross the softening point, achieving firing to the flat glass. As a result, a second heating process at elevated temperatures (e.g., associated with the bending furnace) will not necessarily result in a significant softening of the fired frit. The fired flat assembly may be paired with the mating glass ply with a separating powder and bent with the fired frit on surface 2 or surface 3, as desired. This process has been found to have a high rate of success, as the sticking or fusing and outgas sing issues are lessened.
Pre-firing the frit in this elevated temperature range, however, may also present a number of drawbacks. For example, the capital investment and floor space required for the pre-firing equipment is high. Significant energy is needed to heat the glass to the firing temperature and cool the glass twice. The repeated high-temperature and cooling processes also may inject delays into the process. Additionally, there exists the potential to create optical distortion and residual stress in the glass substrates during the pre-firing process that, in turn, may increase the likelihood of the glass breaking.
Thus, it will be appreciated that there is a need in the art for improved techniques for forming an opaque pattern on a substrate and/or in connection with a glazing for automotive, window, and/or other applications. For instance, it will appreciated that it would be desirable to provide a reliable screen printing process, e.g., in connection with a “direct fire” surface 2 and/or surface 3 applied opaque material, in a manner that is compatible with a double lite bending process, and potentially without the need for pre-firing in the flat state, for use in such applications.
In certain example embodiments of this invention, a method of making a glazing for an automobile is provided. A water-inclusive opacifying agent is screen printed, directly or indirectly, on a major surface of a first glass substrate in a desired pattern in connection with a screen mesh that has at least 200 threads per inch and while maintaining an environment that has a relative humidity of at least 80% over and/or proximate to the screen mesh. The first glass substrate with the opacifying agent thereon is heated to a first temperature sufficient to at least partially cure the opacifying agent in the desired pattern. The first glass substrate and a second glass substrate are bent in connection with a peak temperature higher than the first temperature. The first and second glass substrates are laminated together so that the cured opacifying agent is provided on an interior surface of the glazing.
According to certain example embodiments, the mesh may have at least 200 or at least 230 threads per inch, e.g., where a high resolution pattern is desired.
According to certain example embodiments, the relative humidity in the environment may be 90-95%.
According to certain example embodiments, the peak temperature may be at least twice as high as the first temperature. For example, the first temperature may be less than 200 degrees C. (e.g., about 125-150 degrees C.) and may cause at least a majority (and more preferably, at least 75-95%) of organic components provided in the opacifying agent to be driven off, and the peak temperature may be at least about 600 degrees C. and may cause the opacifying agent to fully cure.
According to certain example embodiments, the first temperature may be about 300 degrees C. and may be held for less than 10 (e.g., about 4) minutes. In such cases, the heating of the first glass substrate with the opacifying agent thereon to the first temperature may fully cure the opacifying agent by driving off all organic components initially provided therein.
According to certain example embodiments, the opacifying agent, when cured, may form an opaque or substantially opaque layer, and the first substrate may have a surface stress less than about 250 psi (more preferably less than about 150 psi) in an area proximate the opaque or substantially opaque layer.
In certain example embodiments of this invention, a method of making a coated article comprising a glass substrate and an opaque film is provided. An opaque paint is screen printed, directly or indirectly, on a major surface of the substrate in a desired pattern, while maintaining an environment with a relative humidity of at least 80% over and/or proximate to a mesh used in the screen printing. The first glass substrate is heated with the opaque paint thereon. The paint has a composition such that it is (a) fully cured when heated to a first temperature of 250-400 degrees, and (b) substantially fully cured when heated to a second temperature below 175 degrees C., in making the coated article.
According to certain example embodiments, at least the substrate with the opaque paint thereon may be bent to a desired shape, with the bending optionally being performed at a third temperature that is at least twice as high as the first temperature and at least three times as high as the second temperature.
According to certain example embodiments, the paint may be pushed through the screen, and the resulting deposit may be controlled, in connection with hydraulic forces that account for a sheer thinning property of the opaque paint, e.g., by balancing squeegee speed, squeegee angle relative to the screen, and/or hardness of the squeegee.
According to certain example embodiments, a method of making a laminated article is provided. A second glass substrate and a coated article made according to the method described three paragraphs above are booked together (optionally with a separator powder therebetween). The second glass substrate and the coated article are bent at a third temperature that is at least twice as high as the first temperature and at least three times as high as the second temperature. The second glass substrate and the coated article are laminated together (e.g., using PVB, EVA, PET, PU, and/or the like) in making the laminated article.
In certain example embodiments of this invention, a method of making a laminated article is provided. An opaque material is printed, directly or indirectly, on a major surface of a first glass substrate in a desired pattern in connection with a mesh that has at least 200 threads per inch. The opaque material is pushed through the screen in connection with hydraulic forces that account for a sheer thinning property of the opaque material by balancing (a) squeegee speed, (b) squeegee angle relative to the screen, and (c) hardness of the squeegee. The first glass substrate with the opaque material thereon is heated to a first temperature sufficient to at least partially cure the opaque material. The first glass substrate and a second glass substrate are bent in connection with a peak temperature higher than the first temperature. The first and second glass substrates are laminated together so that the cured opaque material is provided on an interior surface of the glazing.
These example embodiments, features, aspects, and advantages may be combined in various combinations and sub-combinations to arrive at yet further example embodiments of the invention.